New Dark Matter Model With Late-Time Drag Proposed to Explain Growth Rate Anomalies
Researchers have proposed a new dark matter model called interacting Decaying Cold Dark Matter (iDCDM), in which dark matter experiences a growing drag from dark radiation at late cosmic times, potentially explaining observed suppression in large-scale structure growth. Current measurements of the linear growth rate at redshifts below 1 appear lower than predicted by the standard cosmological model, ΛCDM, motivating alternative explanations. The model adds only two parameters beyond ΛCDM and makes testable predictions for upcoming surveys including DESI, Euclid, and Rubin.
A new preprint posted to arXiv introduces interacting Decaying Cold Dark Matter (iDCDM), a particle physics model designed to address a growing tension between ΛCDM predictions and observed large-scale structure growth at low redshifts. Analyses of fσ8 and weak-lensing data suggest the linear growth rate at z≲1 is lower than the standard model predicts, and iDCDM attempts to explain this by introducing a drag force on dark matter from dark radiation produced through dark matter decay. Unlike conventional dark matter–dark radiation interactions, which weaken as the universe expands, this drag grows stronger at late times, producing a distinctive step-shaped suppression in the growth rate f(k,z) as a function of both scale and redshift. The model preserves agreement with Big Bang nucleosynthesis, the primary cosmic microwave background, and background cosmological evolution, adding only two free parameters. When tested against current data, iDCDM shows a modest statistical preference over ΛCDM, with Δχ² ranging from −2.7 to −7.6 depending on modeling assumptions about the drag's redshift scaling and neutrino masses. The authors identify upcoming scale- and redshift-resolved growth measurements from DESI, Euclid, and the Rubin Observatory as the decisive tests of the model.
What's missing
The paper is a preprint and has not yet undergone peer review. The statistical preference over ΛCDM (Δχ² of −2.7 to −7.6) is modest and dependent on assumptions about neutrino masses and drag scaling, meaning the significance of the result is not yet firmly established. The model's consistency with other cosmological probes beyond fσ8, weak lensing, BBN, and the primary CMB — such as galaxy cluster counts or the Lyman-alpha forest — is not addressed in the abstract.
What different sources said
- arXiv astro-phCenter
Dark Matter with a Drag at Low Redshift
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